Abstract: Twenty sprague-dawley rats aged 8 weeks were randomly divided into 2 groups:1) control (group A, n=10);2) fatigue model (group B, n=10). Fatigue model was established using exercise training of exhausted swimming in group B. 24 h after the last exhausted swimming in group B, femoral artery blood was collected and the concentrations of IFN-γ, IL-4, IL-12, IL-27 in serum were measured using ABC-ELISA. The experimental result indicated:1) Both of the level of serum IFN-γ and IFN-γ/IL-4 in group B were significantly lower than that in group A (P<0.05), but there was no significant difference of serum IL-4 between group B and group A (P<0.05). 2) Serum IL-12 concentration in group B was significantly lower than that in group A (P<0.05). 3) The concentration of serum IL-12 correlated positively with that of serum IFN-γ (P<0.01), but there were no significant correlation between serum IL-27 and IFN-γ, IL-12 and IL-27 (P>0.05) in rats. In conclusions, T1/T2 imbalance in fatigue rats, characterized by T1-type immunosuppression, is related to production of IL-12, but not closely related to production of IL-27.